This invention relates to the treatment of flexible recording elements to eliminate recording layer defects.
Flexible recording elements have found increasing use in several branches of industry. Audio recording tape, for example, is increasingly employed in the sound recording industry as a storage medium for speech and musical compositions. Similarly, video tape has found increasing use in the television industry as a storage medium for television programs. Recently, flexible annular recording discs have been introduced for use as a digital data storage device in the data processing industry.
The above flexible recording elements all share common manufacturing techniques. In a typical manufacturing process, a sheet or roll of durable flexible substrate material, such as Mylar, is coated with a solution having desired magnetic recording characteristics, such as iron oxide contained in a resin binder. After coating, the sheet is subjected to a heat treating step during which the solution is cured by baking or the like. The treated sheet is then trimmed to the appropriate shape by slitting, slicing, or in the case of annular recording discs, by punching or stamping to an annular shape. After trimming, a suitable lubricant is applied to the recording surface, after which the recording element is tested.
The manufacturing yield of such flexible recording elements in the past has suffered from the fact that during the coating process relatively large agglomerated particles or chunks of iron oxide are naturally formed in the recording layer. These agglomerates project outwardly from the recording layer surface and, unless removed, adversely affect the performance of the recording element in the following manner.
The recording and reproduction fidelity of a magnetic recording element is directly related to the separation distance between the recording surface and the associated magnetic transducer. For best results, this separation distance should be substantially invariant as the recording surface sweeps past the transducer. However, when a portion of the recording surface having a projecting agglomerate passes over the surface of the magnetic transducer, the separation distance therebetween is momentarily increased, thereby alterating the strength of the magnetic field penetrating the recording layer during recording or the strength of the field emanating from the recording layer which is sensed by the transducer during reproduction. The result is degradation of the signal and, in severe cases, complete loss of information.
This problem is compounded by the fact that one or more agglomerates can be extracted from the recording layer and attached to the surface of the transducer under typical operating pressures and temperatures. Thereafter, as other portions of the recording surface are swept past the transducer surface, the attached agglomerate cuts into and removes portions of the recording layer. In aggravated cases, such as in digital applications in which the transducer is swept across the surface of a flexible disc element rotating at a high speed, the entire recording layer can be destroyed in a matter of seconds.
An additional problem which serves to impair the manufacturing yield of flexible recording elements of the type noted above is the uneveness of the surface of the recording layer after the curing step is completed. Irregular undulations in the recording surface are known to produce premature wear of the magnetic transducer suface, thus shortening the usful life of this latter element.
Conventional techniques emloyed in the past to improve the recording layer surface characteristics of flexible recording elements include hot or cold pressing between hard or soft rollers, and high speed sanding or polishing with loose abrasive materials in a manner analogous to techniques employed in polishing optical devices. To date, such efforts have met with only limited success.